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One unit can drain at over 400 gallons per hour, although lower flow rates can be more effective in maximising drainage. As water will only flow slowly when low lying, fast water removal causes air to enter the system too quickly, thus terminating the syphonic process. A simple rule of thumb, therefore, is that for fast drainage use a 22mm hose and for more effective drainage use 15mm. A squeegee pushing water across the roof to the syphon head further increases efficiency, with the result that hardly any water remains.

The same can be said for drop between the syphon head and the outlet end of the hose. The longer the drop, the faster the flow. A 5m drop through a 15mm hose is generally a good guide for both efficient and effective drainage. Standard supply has an interchangeable bayonet fitting and 10m of 15mm hose.